You might as well just assume God exists and not need an argument at all.
The ontological argument shows this to be the case. God is evident in his existence and so yes doesn't need an argument.
What the ontological argument does is show more facts beyond that but also, that not only do we see it exists, but can't conceive of it not existing. It exists necessarily. But it shows, we can't even say perhaps it doesn't exist, perhaps it's in my imagination, because it's Necessity shows it's not for sure.
We see ourselves exist. But we know we don't exist necessarily, we are contingent beings. Our parents could've never met (naturalism wise) and we would not exist.
God is seen to exist true by this argument and so its seem redundant. But the argument is showing for skeptics, the idea of God is not a mere idea, you can't divorce existence from it because it's vastness and greatness implies it exists. This is known through the concept of Necessary existence.